Air separation control system and control method

ABSTRACT

The present invention discloses an air separation control system and control method comprising: multiple air separation plants for air separation; multiple local controllers, respectively corresponding to the multiple air separation plants; each local controller being located locally at the air separation plant corresponding thereto, and being in communicative connection with the corresponding air separation plant, for the purpose of locally controlling the air separation plant; and a remote optimization controller, in communicative connection with each local controller separately; the remote optimization controller at least comprising a communication module, a prediction module and a control module; the remote optimization controller being able to perform data exchange with and predictive control of the multiple air separation plants simultaneously via the local controllers. The present invention controls multiple air separation plants located at different locations via a remote optimization controller, thus reducing the professional competence requirements placed on operators; during optimization, the relationship between multiple air separation plants can be considered as a whole, so that the air separation plants operate smoothly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119(a) and (b) to Chinese patent application No. CN20201160931.2, filedDec. 30, 2020 and published as CN 112783034 on May 11, 2021, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of control systems, inparticular to an air separation control system and control method.

BACKGROUND OF THE INVENTION

Adjustment and optimization of the operating process of an airseparation plant generally rely on an operator to adjust a local controlsystem in communicative connection with the air separation plant or anadvanced control system in a local computer; thus, both operation andmaintenance of the air separation plant need to be carried out locallyat the air separation plant. Optimization, upgrading and programming ofthe local control system or the advanced control system in the localcomputer also need to be performed locally at the air separation plant.This places higher requirements on the ability of the local operator toadjust the local control system or advanced control system. Multiple airseparation plants might be located at different sites, and in order toensure the operational effectiveness and operating safety of the airseparation plants, a professional operator must be provided at each airseparation plant. However, due to a shortage of operators or a low levelof technical ability amongst operators, the adjustment and optimizationof air separation plant operation cannot meet actual needs.

The intellectual property information stored in the local control systemor the advanced control system in the local computer is also at risk ofbeing leaked, thus causing losses.

SUMMARY OF THE INVENTION

The objective of certain embodiments of the present invention is toprovide an air separation control system and control method, wherein aremote optimization controller is provided, so as to intervene in andoptimize the operation of multiple air separation plants.

In order to achieve the above objective, certain embodiments of thepresent invention provides an air separation control system that caninclude: multiple air separation plants for air separation; multiplelocal controllers, corresponding to the multiple air separation plants;each local controller being located locally at the air separation plantcorresponding thereto, and being in communicative connection with thecorresponding air separation plant, for the purpose of controlling theair separation plant; and a remote optimization controller, incommunicative connection with each local controller separately.

In preferred embodiments, the remote optimization controller can includea communication module, a prediction module and a control module; andthe remote optimization controller being able to perform data exchangewith and predictive control of the multiple air separation plantssimultaneously via the local controllers.

Preferably, the remote optimization controller is provided at a fixedlocation, being situated at a location local to any one air separationplant or a location different from that of each of the multiple airseparation plants.

Preferably, the remote optimization controller determines a controlledvariable, an operating variable and a disturbance variable according toan optimization target parameter of each air separation plant, andestablishes predictive control models separately on this basis.

Preferably, the remote optimization controller further comprises a datastorage module for storing operating data; the operating data comprisescurrently collected real-time data and historical data of all of the airseparation plants.

Preferably, the communication module is configured to be incommunicative connection with each local controller separately, receivethe currently collected real-time data, and send an operatinginstruction to the local controller;

the prediction module predicts a value of the controlled variableaccording to the predictive control model, historical data and real-timedata, adjusts the operating variable according to the value, andprovides feedback to the control module;

the control module generates an operating instruction for regulating airseparation plant operation according to the feedback of the predictionmodule;

the control module sends the operating instruction to provide feedbackto the local controller at the air separation plant via thecommunication module, and adjusts a value of the operating variable viathe local controller; by adjusting the value of the operating variable,the controlled variable is kept within a preset range and as close to anoptimal value as possible at the current time and for a future period oftime; at the same time, a change in value of the disturbance variablewill cause the predicted value of the controlled variable to change, andin order to ensure that the controlled variable is always within thepreset range, the operating variable will be adjusted correspondingly.

Preferably, the controlled variable comprises any one or more of thefollowing: temperature, pressure, flow rate, liquid level, andcomponents.

Preferably, the optimization target parameter comprises any one or moreof the following: extraction rate of oxygen, extraction rate ofnitrogen, extraction rate of argon, gaseous oxygen product purity,gaseous nitrogen product purity and gaseous argon product purity.

Preferably, the air separation plant at least comprises a high-pressurecolumn, a low-pressure column, a crude argon column, an air compressorand an air expander.

Preferably, the controlled variable comprises an oxygen content at anargon fraction extraction port of the low-pressure column, an oxygencontent in a middle region of the crude argon column, a temperature infront of the air expander, and an argon component, etc.; the operatingvariable comprises a gaseous oxygen product flow rate, a total air flowrate into the high-pressure column, a high-pressure air flow rate, anexpanded air quantity, and a crude argon liquid flow rate; and thedisturbance variable comprises a liquid nitrogen flow rate, amedium-pressure nitrogen gas flow rate, a gaseous oxygen product flowrate, and a gaseous argon product flow rate.

Preferably, the remote optimization controller can adjust the predictivecontrol model according to historical data and real-time data.

Preferably, a safe mode is included: the preset range of the controlledvariable is provided in the data storage module; the remote optimizationcontroller breaks the communication connection between the remoteoptimization controller and the local controller when the controlledvariable exceeds the preset range, and the local controller directlycontrols the air separation plant.

Preferably, the air separation control system can switch operationbetween an optimized mode and a non-optimized mode;

in the optimized mode, the local controller collects the operating data,and regulates the operation of the air separation plant according to anoperating instruction provided by the remote optimization controller;

in the non-optimized mode, the local controller blocks an operatinginstruction coming from the remote optimization controller, and thelocal controller independently regulates the operation of the airseparation plant locally.

Preferably, after receiving an operating instruction of the remoteoptimization controller, the local controller switches to thenon-optimized mode in which the local controller independently regulatesthe operation of the air separation plant locally;

alternatively, the local controller regulates the operation of the airseparation plant according to an operating instruction provided by theremote optimization controller, and continues to collect operating dataof the air separation plant and send it to the remote optimizationcontroller for further optimization; and the optimized mode is executedcyclically until it is switched to the non-optimized mode in which thelocal controller independently regulates the operation of the airseparation plant locally.

Preferably, regulating the operation of the air separation plant atleast comprises controlling a start operation, a stop operation, allcontrol loops and a safety interlock device.

Preferably, the start operation, stop operation, all control loops andsafety interlock device of the air separation plant are kept at a locallevel, and are controlled by the local controller.

Preferably, the remote optimization controller provides an operatinginstruction according to operating data collected by one or more localcontrollers; the remote optimization controller feeds the operatinginstruction back to the local controller that provided operating datathereto, or feeds the operating instruction back to all of the localcontrollers in communicative connection therewith.

Certain embodiments of the present invention also provide a controlmethod for an air separation control system, suitable for the airseparation control system described, and comprising: a remoteoptimization controller determining a controlled variable, an operatingvariable and a disturbance variable according to an optimization targetparameter, and establishing a predictive control model; receivingcurrently collected real-time data from a local controller, while a datastorage module stores operating data; predicting a value of thecontrolled variable according to the predictive control model,historical data and real-time data, and providing feedback to a controlmodule; the control module generating an operating instruction forregulating air separation plant operation according to feedback of aprediction module; the operating instruction being fed back to the localcontroller at the air separation plant via the communication module, anda value of the operating variable being adjusted via the localcontroller; by adjusting the value of the operating variable, thecontrolled variable is kept within a preset range and as close to anoptimal value as possible at the current time and for a future period oftime; at the same time, a change in value of the disturbance variablewill cause the predicted value of the controlled variable to change, andin order to ensure that the controlled variable is always within thepreset range, the operating variable will be adjusted correspondingly;regulating the operation of the air separation plant according to theoperating instruction.

The beneficial effects of certain embodiments of the present inventionare as follows:

The air separation control system provided by certain embodiments of thepresent invention controls multiple air separation plants located atdifferent positions via a remote optimization controller, thus reducingthe professional competence requirements placed on operators; whileadjusting and optimizing each air separation plant, the remoteoptimization controller also performs self-optimization of thepredictive control model, thus achieving effective coupling ofartificial intelligence to the air separation plants; duringoptimization, the relationship between multiple air separation plantscan be considered as a whole, so that the air separation plants operatesmoothly. At the same time, intellectual property information is storedin the remote optimization controller with a high level ofconfidentiality; this can reduce the risk of information leakage andadvantageously protects the intellectual property information of the airseparation plants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the air separation control system ofthe present invention.

FIG. 2 is a flow chart of the control method for the air separationcontrol system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The technical solution of the present invention will be clearly andcompletely described below in conjunction with the accompanyingdrawings. Obviously, the described embodiments are some of theembodiments of the present invention, rather than all of theembodiments. Based on the embodiments of the present invention, allother embodiments obtained by those of ordinary skill in the art withoutcreative work shall fall within the protection scope of the presentinvention.

As shown in FIG. 1, the air separation control system provided bycertain embodiments of the present invention comprises multiple airseparation plants for air separation; the air separation plant at leastcomprises a high-pressure column, a low-pressure column, a crude argoncolumn, an air compressor and an air expander. Multiple localcontrollers correspond to the multiple air separation plants; each localcontroller is located locally at the air separation plant correspondingthereto, and is in communicative connection with the corresponding airseparation plant, for the purpose of controlling the air separationplant; optionally, the local controller can be a DCS (distributedcontrol system)/PLC (programmable logic controller)/SIS (safetyinstrumented control system). A remote optimization controller is incommunicative connection with each local controller separately; theremote optimization controller can perform data exchange with andpredictive control of the multiple air separation plants simultaneouslyvia the local controller; and the remote optimization controller isprovided at a fixed location, being situated at a location local to acertain air separation plant, or a location different from that of eachof the multiple air separation plants.

The remote optimization controller comprises a communication module, aprediction module, a control module and a data storage module. Theprediction module first determines controlled variables, operatingvariables and disturbance variables according to optimization targetparameters of each air separation plant, and establishes predictivecontrol models separately on this basis; moreover, the predictivecontrol model is capable of continuous self-adjustment according tohistorical data and real-time data.

The controlled variables are process parameters in the air separationplants that are required to be kept within a preset range; the operatingvariables are process parameters that are operated by the localcontrollers and used to overcome the influence of interference so as tokeep the controlled variables within the preset range and as close aspossible to optimal values; and the disturbance variables are factorsthat are not operating variables, but act on the air separation plantsand cause the controlled variables to change. The controlled variablesinclude any one or more of the following: temperature, pressure, flowrate, liquid level, and components.

The communication module is in communicative connection with each localcontroller separately, and receives values of the controlled variables,operating variables and disturbance variables collected in real time bythe local controllers as real-time data, which is transmitted to theremote optimization controller and stored in the data storage module.The predictive control model is based on an algorithm, and predictsvalues of the controlled variables according to the real-time datacollected on this occasion and historical data collected previously,adjusts the operating variables according to these values, and feeds thecontrolled variables back to the control module.

The control module generates operating instructions for regulating theoperation of the air separation plants according to the feedback of theprediction module, sends the operating instructions to the localcontrollers via the communication module, and adjusts the values of theoperating variables via the local controllers. By adjusting the valuesof the operating variables, the controlled variables are kept within thepreset range and as close to the optimal values as possible at thecurrent time and for a future period of time. At the same time, changesin the values of the disturbance variables will cause the predictedvalues of the controlled variables to change.

In order to ensure that the controlled variables are always within thepreset range, the operating variables will be adjusted correspondingly.The data storage module is used to store operating data, which includesthe real-time data collected on this occasion by the communicationmodule and the historical data collected previously. The preset range ofthe controlled variables is also provided in the data storage module.

In some embodiments, the optimization target parameters include any oneor more of the following: oxygen extraction rate, nitrogen extractionrate, argon extraction rate, gaseous oxygen product purity, gaseousnitrogen product purity, and gaseous argon product purity. Thecontrolled variables include the oxygen content at the argon fractionextraction port of the low-pressure column, oxygen content in a middleregion of the crude argon column, temperature in front of the airexpander, and argon component, etc.; the operating variables include thegaseous oxygen product flow rate, total air flow rate into thehigh-pressure column, high-pressure air flow rate, expanded airquantity, and crude argon liquid flow rate; and the disturbancevariables include the liquid nitrogen flow rate, medium-pressurenitrogen gas flow rate, gaseous oxygen product flow rate, and gaseousargon product flow rate.

The modes of operation of the air separation control system provided bycertain embodiments of the present invention include an optimized modeand a non-optimized mode; the air separation control system can switchoperation between the optimized mode and the non-optimized mode.

In the optimized mode, the local controllers collect the operating data,and regulate the operation of the air separation plants according to theoperating instructions provided by the remote optimization controller.

In the non-optimized mode, the local controllers block the operatinginstructions coming from the remote optimization controller, and thelocal controllers independently regulate the operation of the airseparation plants locally. In some embodiments, after receiving anoperating instruction of the remote optimization controller, the localcontroller switches to the non-optimized mode in which the localcontroller independently regulates the operation of the air separationplant locally.

In other embodiments, the local controllers regulate the operation ofthe air separation plants according to the operating instructionsprovided by the remote optimization controller, and continue to collectoperating data of the air separation plants and send it to the remoteoptimization controller for further optimization; and the optimized modeis cyclically executed until it is switched to the non-optimized mode inwhich the local controller independently regulates the operation of theair separation plant locally.

When the control system for the air separation plants is operating inthe optimized mode, the control module is allowed to read the datastorage module. When a controlled variable exceeds the preset range, thecommunication connection between the remote optimization controller andthe local controller is broken, and the optimized mode is switched to asafe mode, with the local controller directly controlling the airseparation plant.

In some embodiments, regulating the operation of the air separationplants at least includes controlling a start operation, a stopoperation, all control loops, and a safety interlock device. The startoperation, stop operation, all control loops and safety interlock deviceare kept at the local level, controlled by the local controller.

In some embodiments, the remote optimization controller providesoperating instructions according to the operating data collected by oneor more local controllers; the remote optimization controller feeds theoperating instructions back to the local controller that provided theoperating data thereto, or feeds the operating instructions back to allof the local controllers in communicative connection therewith.

As shown in FIG. 2, a control method for the air separation controlsystem of the present invention is as follows:

The remote optimization controller determines the controlled variables,operating variables and disturbance variables according to theoptimization target parameters, and establishes a predictive controlmodel.

Currently collected real-time data is received from the localcontrollers, and the data storage module stores operating data at thesame time.

The values of the controlled variables are predicted according to thepredictive control model, historical data and real-time data, and fedback to the control module.

The control module generates operating instructions for regulating theoperation of the air separation plants according to the feedback of theprediction module; the operating instruction being fed back to the localcontroller at the air separation plant via the communication module, anda value of the operating variable being adjusted via the localcontroller; by adjusting the value of the operating variable, thecontrolled variable is kept within a preset range and as close to anoptimal value as possible at the current time and for a future period oftime; at the same time, a change in value of the disturbance variablewill cause the predicted value of the controlled variable to change, andin order to ensure that the controlled variable is always within thepreset range, the operating variable will be adjusted correspondingly.

The operation of the air separation plant is regulated according to theoperating instructions.

In summary, the air separation control system and control method asprovided by certain embodiments of the present invention controlmultiple air separation plants located at different locations via aremote optimization controller, thus reducing the professionalcompetence requirements placed on operators; during optimization, therelationship between multiple air separation plants can be considered asa whole, so that the air separation plants operate smoothly. At the sametime, intellectual property information is stored in the remoteoptimization controller, so the risk of information leakage can bereduced.

Although the content of the present invention has been presented indetail by means of the preferred embodiments above, it should berecognized that the description above should not be considered as alimitation of the present invention. Various amendments andsubstitutions to the present invention will be apparent after perusal ofthe above content by those skilled in the art. Thus, the scope ofprotection of the present invention should be defined by the attachedclaims.

While the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in light of the foregoing description. Accordingly, it is intendedto embrace all such alternatives, modifications, and variations as fallwithin the spirit and broad scope of the appended claims. The presentinvention may suitably comprise, consist or consist essentially of theelements disclosed and may be practiced in the absence of an element notdisclosed. Furthermore, if there is language referring to order, such asfirst and second, it should be understood in an exemplary sense and notin a limiting sense. For example, it can be recognized by those skilledin the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means thesubsequently identified claim elements are a nonexclusive listing (i.e.,anything else may be additionally included and remain within the scopeof “comprising”). “Comprising” as used herein may be replaced by themore limited transitional terms “consisting essentially of” and“consisting of” unless otherwise indicated herein.

“Providing” in a claim is defined to mean furnishing, supplying, makingavailable, or preparing something. The step may be performed by anyactor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

All references identified herein are each hereby incorporated byreference into this application in their entireties, as well as for thespecific information for which each is cited.

In the figures:

1—air separation unit,

2—local controller,

3—remote optimization controller.

We claim:
 1. Air separation control system comprising: multiple airseparation plants configured to separate air via cryogenic distillation;multiple local controllers, corresponding to the multiple air separationplants; each local controller being located locally at the airseparation plant corresponding thereto, and being in communicativeconnection with the corresponding air separation plant, for the purposeof controlling the air separation plant; and a remote optimizationcontroller, in communicative connection with each local controllerseparately; wherein the remote optimization controller comprises acommunication module, a prediction module and a control module; whereinthe remote optimization controller is configured to perform dataexchange with and predictive control of the multiple air separationplants simultaneously via the local controllers.
 2. The air separationcontrol system according to claim 1, wherein the remote optimizationcontroller is provided at a fixed location, being situated at a locationlocal to any one air separation plant or a location different from thatof each of the multiple air separation plants.
 3. The air separationcontrol system according to claim 1, wherein the remote optimizationcontroller determines a controlled variable, an operating variable and adisturbance variable according to an optimization target parameter ofeach air separation plant, and establishes predictive control modelsseparately on this basis.
 4. The air separation control system accordingto claim 3, wherein the remote optimization controller further comprisesa data storage module for storing operating data; the operating datacomprises currently collected real-time data and historical data of allof the air separation plants.
 5. The air separation control systemaccording to claim 4, wherein the communication module is configured tobe in communicative connection with each local controller separately,receive the currently collected real-time data, and send an operatinginstruction to the local controller; the prediction module predicts avalue of the controlled variable according to the predictive controlmodel, historical data and real-time data, adjusts the operatingvariable according to the value, and provides feedback to the controlmodule; the control module generates an operating instruction forregulating air separation plant operation according to the feedback ofthe prediction module; the control module sends the operatinginstruction to provide feedback to the local controller at the airseparation plant via the communication module, and adjusts a value ofthe operating variable via the local controller; by adjusting the valueof the operating variable, the controlled variable is kept within apreset range and as close to an optimal value as possible at the currenttime and for a future period of time; at the same time, a change invalue of the disturbance variable will cause the predicted value of thecontrolled variable to change, and in order to ensure that thecontrolled variable is always within the preset range, the operatingvariable will be adjusted correspondingly.
 6. The air separation controlsystem according to claim 3, wherein the controlled variable comprisesany one or more of the following: temperature, pressure, flow rate,liquid level, and components.
 7. The air separation control systemaccording to claim 3, wherein the optimization target parametercomprises any one or more of the following: extraction rate of oxygen,extraction rate of nitrogen, extraction rate of argon, gaseous oxygenproduct purity, gaseous nitrogen product purity and gaseous argonproduct purity.
 8. The air separation control system according to claim6, wherein the air separation plant at least comprises a high-pressurecolumn, a low-pressure column, a crude argon column, an air compressorand an air expander.
 9. The air separation control system according toclaim 8, wherein the controlled variable comprises an oxygen content atan argon fraction extraction port of the low-pressure column, an oxygencontent in a middle region of the crude argon column, a temperature infront of the air expander, and an argon component, etc.; the operatingvariable comprises a gaseous oxygen product flow rate, a total air flowrate into the high-pressure column, a high-pressure air flow rate, anexpanded air quantity, and a crude argon liquid flow rate; and thedisturbance variable comprises a liquid nitrogen flow rate, amedium-pressure nitrogen gas flow rate, a gaseous oxygen product flowrate, and a gaseous argon product flow rate.
 10. The air separationcontrol system according to claim 4, wherein the remote optimizationcontroller can adjust the predictive control model according tohistorical data and real-time data.
 11. The air separation controlsystem according to claim 5, further comprising a safe mode: the presetrange of the controlled variable is provided in the data storage module;the remote optimization controller breaks the communication connectionbetween the remote optimization controller and the local controller whenthe controlled variable exceeds the preset range, and the localcontroller directly controls the air separation plant.
 12. The airseparation control system according to claim 1, wherein the airseparation control system can switch operation between an optimized modeand a non-optimized mode; in the optimized mode, the local controllercollects the operating data, and regulates the operation of the airseparation plant according to an operating instruction provided by theremote optimization controller; in the non-optimized mode, the localcontroller blocks an operating instruction coming from the remoteoptimization controller, and the local controller independentlyregulates the operation of the air separation plant locally.
 13. The airseparation control system according to claim 12, wherein after receivingan operating instruction of the remote optimization controller, thelocal controller switches to the non-optimized mode in which the localcontroller independently regulates the operation of the air separationplant locally.
 14. The air separation control system according to claim12, wherein the local controller is configured to regulate the operationof the air separation plant according to an operating instructionprovided by the remote optimization controller, and continues to collectoperating data of the air separation plant and send the operating datato the remote optimization controller for further optimization; and theoptimized mode is executed cyclically until it is switched to thenon-optimized mode in which the local controller independently regulatesthe operation of the air separation plant locally.
 15. The airseparation control system according to claim 12, wherein regulating theoperation of the air separation plant at least comprises controlling astart operation, a stop operation, all control loops and a safetyinterlock device.
 16. The air separation control system according toclaim 15, wherein the start operation, stop operation, all control loopsand safety interlock device of the air separation plant are kept at alocal level, and are controlled by the local controller.
 17. The airseparation control system according to claim 5, wherein the remoteoptimization controller provides an operating instruction according tooperating data collected by one or more local controllers; the remoteoptimization controller feeds the operating instruction back to thelocal controller that provided operating data thereto, or feeds theoperating instruction back to all of the local controllers incommunicative connection therewith.
 18. A control method for airseparation control system, suitable for control of the air separationsystem according to claim 1, the method comprising the steps of:providing a remote optimization controller that is configured todetermine a controlled variable, an operating variable and a disturbancevariable according to an optimization target parameter, and establishinga predictive control model; receiving currently collected real-time datafrom a local controller, while a data storage module stores operatingdata; predicting a value of the controlled variable according to thepredictive control model, historical data and real-time data, andproviding feedback to a control module; generating an operatinginstruction for regulating air separation plant operation according tofeedback of a prediction module using the control module; the operatinginstruction being fed back to the local controller at the air separationplant via the communication module, and a value of the operatingvariable being adjusted via the local controller; by adjusting the valueof the operating variable, the controlled variable is kept within apreset range and as close to an optimal value as possible at the currenttime and for a future period of time; at the same time, a change invalue of the disturbance variable will cause the predicted value of thecontrolled variable to change, and in order to ensure that thecontrolled variable is always within the preset range, the operatingvariable will be adjusted correspondingly; and regulating the operationof the air separation plant according to the operating instruction.